package craky.security;

import java.util.zip.Checksum;

public class CRC16
  implements Checksum
{
  private static final int[] CRC_TABLE = { 0, 49345, 49537, 320, 49921, 960, 640, 49729, 50689, 
    1728, 1920, 51009, 1280, 50625, 50305, 1088, 52225, 3264, 3456, 52545, 3840, 
    53185, 52865, 3648, 2560, 51905, 52097, 2880, 51457, 2496, 2176, 51265, 55297, 
    6336, 6528, 55617, 6912, 56257, 55937, 6720, 7680, 57025, 57217, 8000, 56577, 
    7616, 7296, 56385, 5120, 54465, 54657, 5440, 55041, 6080, 5760, 54849, 53761, 
    4800, 4992, 54081, 4352, 53697, 53377, 4160, 61441, 12480, 12672, 61761, 13056, 
    62401, 62081, 12864, 13824, 63169, 63361, 14144, 62721, 13760, 13440, 62529, 15360, 
    64705, 64897, 15680, 65281, 16320, 16000, 65089, 64001, 15040, 15232, 64321, 14592, 
    63937, 63617, 14400, 10240, 59585, 59777, 10560, 60161, 11200, 10880, 59969, 60929, 
    11968, 12160, 61249, 11520, 60865, 60545, 11328, 58369, 9408, 9600, 58689, 9984, 
    59329, 59009, 9792, 8704, 58049, 58241, 9024, 57601, 8640, 8320, 57409, 40961, 
    24768, 24960, 41281, 25344, 41921, 41601, 25152, 26112, 42689, 42881, 26432, 42241, 
    26048, 25728, 42049, 27648, 44225, 44417, 27968, 44801, 28608, 28288, 44609, 43521, 
    27328, 27520, 43841, 26880, 43457, 43137, 26688, 30720, 47297, 47489, 31040, 47873, 
    31680, 31360, 47681, 48641, 32448, 32640, 48961, 32000, 48577, 48257, 31808, 46081, 
    29888, 30080, 46401, 30464, 47041, 46721, 30272, 29184, 45761, 45953, 29504, 45313, 
    29120, 28800, 45121, 20480, 37057, 37249, 20800, 37633, 21440, 21120, 37441, 38401, 
    22208, 22400, 38721, 21760, 38337, 38017, 21568, 39937, 23744, 23936, 40257, 24320, 
    40897, 40577, 24128, 23040, 39617, 39809, 23360, 39169, 22976, 22656, 38977, 34817, 
    18624, 18816, 35137, 19200, 35777, 35457, 19008, 19968, 36545, 36737, 20288, 36097, 
    19904, 19584, 35905, 17408, 33985, 34177, 17728, 34561, 18368, 18048, 34369, 33281, 
    17088, 17280, 33601, 16640, 33217, 32897, 16448 };
  private int crc;

  public long getValue()
  {
    return this.crc & 0xFFFFFFFF;
  }

  public void reset()
  {
    this.crc = 0;
  }

  public void update(int b)
  {
    this.crc = update(this.crc, b);
  }

  public void update(byte[] b, int off, int len)
  {
    if (b == null)
    {
      throw new NullPointerException();
    }
    if ((off < 0) || (len < 0) || (off > b.length - len))
    {
      throw new ArrayIndexOutOfBoundsException();
    }

    this.crc = updateBytes(this.crc, b, off, len);
  }

  public void update(byte[] b)
  {
    this.crc = updateBytes(this.crc, b, 0, b.length);
  }

  private int update(int crc, int b)
  {
    crc = crc >>> 8 ^ CRC_TABLE[((crc ^ b) & 0xFF)];
    return crc;
  }

  private int updateBytes(int crc, byte[] b, int off, int len)
  {
    for (int i = off; i < off + len; i++)
    {
      crc = update(crc, b[i]);
    }

    return crc;
  }
}